[sdiy] VSM201 Vocorder Question

[rsdio at audiobanshee.com]

A PIC that runs at 48 MHz, e.g., for USB, can manage a 46.875 kHz PWM rate. That's enough to just satisfy Nyquist. Unfortunately, the filter would probably cost more than a true VCA, but if there are cheap low-pass filters oriented towards Compact Disc 44.1 kHz sampling then you might be able to pull it off.

WIthout a fancy, brick-wall filter, you'd lose the ideal 20 kHz bandwidth and drop into the audible range, which 31 kHz certainly would require.

Are you using a PIC that runs at only 32 MHz?

Brian


On Jan 2, 2016, at 12:44 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> I've thought about this a bit because of using the PIC's PWM module so much. The best case output from that is either 8-bit or 10-bit, which means that -60dB is about as good as I'd get using it for a VCA, and that implies having a switching frequency which is much too low (31KHz) for many jobs.